Scanning based technology is common in various industries. For instance, paper products are commonly made using scanning based technology. In this industry, it is common to use scanning technology in order to measure “dirt” counts in paper products such as tissue and towel products. Dirt may be residual ink or other dark specks that are present in a predominantly light colored paper product.
Dirt count measurements typically employ a scanner to obtain raw data. As shown in FIG. 1, a scanner 10 typically has a glass scanner bed 14 located thereon. A target 12 is placed on the glass scanner bed 14, and a light 16, which is typically a bright, cold white light, is used to illuminate the target 12 that is to be scanned. The scanner 10 is typically attached to a host PC which has software that controls the resolution, color mode, scanning area, gamma factors, transform functions, etc. of the scanning process. The light 16 is usually mounted on a moving rack and moves slowly across the glass scanner bed 14. A scanning head 18 is present and consists of an array of light sensitive CCD cells that generate an electrical charge when hit by light. The brighter the light that hits a single CCD cell, the larger the electrical charge the cell will generate. The electrical charge is then converted into a gray scale number which represents the light intensity reflected by the target 12 at a particular point. Gray scale numbers are commonly known in scanning and photographic industries. However, there is no industry wide calibration as to which gray scale value is to be assigned to a target having a particular reflectivity. Typically, a zero gray scale reference number represents the absence of light, and a 255 gray scale number represents complete reflectivity. A drive 20 may be present which converts the raw data from the electrical charge or gray scale number into a format that may be displaced on an output device. Additionally, this data may be transferred into the corresponding PC or saved in a file.
Scanners on the market are primarily designed for the reproduction of photographs, and are not specifically designed as a measurement device to be used to measure the dirt count of paper products. As such, it is sometimes the case that standardization and calibration of scanners may not be possible in order to analyze the dirt count of paper products. Scanners made by different manufacturers and even scanners made by the same manufacturer may assign different gray scale numbers to the identical target 12. As such, when scanners from different manufacturers are used to measure dirt count, without proper adjustment to the scanners, the test results may be incomparable to one another. This discrepancy would cause problems in manufacturing environments that use different scanners in different lines or at different plants. The gray scale response, and hence the dirt count of the paper products, would not be consistent and hence final products of different quality would be produced.
When scanning a paper product, after the entire image of the target 12 is received by the supporting software, the software typically divides all of the pixels received into two groups based on a predetermined threshold value or detection level. Pixels are basic elements for any digital image. The gray level of the pixel may be measured along with the size of the pixel. Pixels that have the gray scale value fall below the threshold value or detection level are classified as containing dirt. Pixels whose gray scale values are higher than the threshold value or detection level are classified as being part of the background of the paper product. The physical size of dirt specks may be hard to measure due to an edge effect in which the dirt speck only partially covers one or more pixels. Therefore, it is sometimes the case that the digitized image of the dirt speck is always larger or smaller than the actual dirt speck due to the edge effect and also due to the detection level or threshold value that is set. The software may compute many values upon the scanning of the target 12. For instance, the average gray scale value may be calculated along with the parts per million (ppm) of the total dirt speck area, and the total number of dirt specks detected.
Scanners 10 may also suffer from variations in movement of the scanning head 18. Slight imprecision in the movement control of the scanning head 18 may cause for varying results when the target 12 is scanned multiple times under the same conditions. Additionally, changes in the light 16 imparted onto the target 12 during scanning may also provide variability upon results that are obtained from scanning the same target 12 multiple times.
Lighting differences can arise from sources including the intensity of the light 16, the angular incidents of the light 16, the temperature of the light 16, and variable light intensity when the scanner 10 is subjected to light variations from an ambient source.
Scanning allows for the quality control of the tissue or towel product that is created. Also, scanning allows for a process control during the manufacturing of the tissue or hand towel. For instance, if there is too much dirt present, the product may be reprocessed or may be treated with a bleaching agent or have virgin fiber blended therein in order to reduce the amount of dirt.
Although many variables are present that may account for measurement errors in the dirt count calculation of a tissue or towel product, it is still possible to achieve statistically acceptable results if dirt specks are analyzed under controlled conditions which include proper settings for the scanner 10.
The present invention seeks to improve the repeatability of dirt count measurements by adjusting the gray scale response between different types of scanners that are used in producing tissues and towel products in different manufacturing plants and/or different areas of the same manufacturing plant. The present invention may be used in the processing of recycled fiber from copy paper, printing paper and newspaper, but it is not limited to this application.